The present invention relates generally to moving target indicator systems for separating radar or sonar moving target echoes from the echoes from non or slowly moving clutter. More particularly, the present invention relates to an MTI system for removing clutter with a minimum amount of hardware.
In general, a radar or sonar signal processing system is designed to reduce the presence of undesired signals received together with desired signals. In the case of an MTI system, the received radar or sonar return pulses include desired moving target reflections and undesired clutter from the sea surface, slow moving rain squalls. chaff, etc. The radar clutter, because of its low or non-existent velocity component, is correlated from pulse to pulse. However, moving targets above a certain velocity have a measurable phase change from pulse to pulse and thus are uncorrelated. The purpose of the MTI system is to cancel all correlated signals on a pulse to-pulse basis, thus cancelling clutter while passing uncorrelated signals such as moving target reflections.
It is known however, that if M uncorrelated clutter sources contribute to the signal, then (M+1) pulses must be utilized to cancel these M clutter contributions. Accordingly, M separate auxiliary channels are required in order to optimally cancel all clutter components between a main signal and a set of M uncorrelated samples.
A variety of systems are currently available for optimally separating moving target echoes from clutter echoes via the use of adaptive filter banks employing matrix inverse or maximum entropy algorithms. However, each of these systems requires a separate set of circuitry for each auxiliary channel thus requiring a large amount of expensive and complex hardware. Accordingly, such systems for removing M sources of correlated clutter are extremely bulky and impractical for use in many radar and sonar environments.